9,138 research outputs found
A unified approach to blending of constant and varying parametric surfaces with curvature continuity
In this paper, we develop a new approach to blending of
constant and varying parametric surfaces with curvature
continuity. We propose a new mathematical model consisting of a
vector-valued sixth-order partial differential equation (PDE) and
time-dependent blending boundary constraints, and develop an
approximate analytical solution of the mathematical model. The
good accuracy and high computational efficiency are
demonstrated by comparing the new approximate analytical
solution with the corresponding accurate closed form solution. We also investigate the influence of the second partial derivatives on
the continuity at trimlines, and apply the new approximate
analytical solution in blending of constant and varying parametric
surfaces with curvature continuit
A qubit strongly-coupled to a resonant cavity: asymmetry of the spontaneous emission spectrum beyond the rotating wave approximation
We investigate the spontaneous emission spectrum of a qubit in a lossy
resonant cavity. We use neither the rotating-wave approximation nor the Markov
approximation. The qubit-cavity coupling strength is varied from weak, to
strong, even to lower bound of the ultra-strong. For the weak-coupling case,
the spontaneous emission spectrum of the qubit is a single peak, with its
location depending on the spectral density of the qubit environment. Increasing
the qubit-cavity coupling increases the asymmetry (the positions about the
qubit energy spacing and heights of the two peaks) of the two spontaneous
emission peaks (which are related to the vacuum Rabi splitting) more.
Explicitly, for a qubit in a low-frequency intrinsic bath, the height asymmetry
of the splitting peaks becomes larger, when the qubit-cavity coupling strength
is increased. However, for a qubit in an Ohmic bath, the height asymmetry of
the spectral peaks is inverted from the same case of the low-frequency bath,
when the qubit is strongly coupled to the cavity. Increasing the qubit-cavity
coupling to the lower bound of the ultra-strong regime, the height asymmetry of
the left and right peak heights are inverted, which is consistent with the same
case of low-frequency bath, only relatively weak. Therefore, our results
explicitly show how the height asymmetry in the spontaneous emission spectrum
peaks depends not only on the qubit-cavity coupling, but also on the type of
intrinsic noise experienced by the qubit.Comment: 10pages, 5 figure
An accuracy measurement method for star trackers based on direct astronomic observation.
Star tracker is one of the most promising optical attitude measurement devices and it is widely used in spacecraft for its high accuracy. However, how to realize and verify such an accuracy remains a crucial but unsolved issue until now. The authenticity of the accuracy measurement method of a star tracker will eventually determine the satellite performance. A new and robust accuracy measurement method for a star tracker based on the direct astronomical observation is proposed here. In comparison with the conventional method with simulated stars, this method utilizes real navigation stars as observation targets which makes the measurement results more authoritative and authentic. Transformations between different coordinate systems are conducted on the account of the precision movements of the Earth, and the error curves of directional vectors are obtained along the three axes. Based on error analysis and accuracy definitions, a three-axis accuracy evaluation criterion has been proposed in this paper, which could determine pointing and rolling accuracy of a star tracker directly. Experimental measurements confirm that this method is effective and convenient to implement. Such a measurement environment is close to the in-orbit conditions and it can satisfy the stringent requirement for high-accuracy star trackers.This work was financially supported by the National High Technology Research and Development Program of China (863 Program) (No. 2012AA121503), National Natural Science Foundation of China (No. 61377012 and No. 51522505) and the China Postdoctoral Science Foundation (No. 2015M570091).This is the final version of the article. It first appeared from Nature Publishing Group via http://dx.doi.org/10.1038/srep2259
Effects of critical temperature inhomogeneities on the voltage-current characteristics of a planar superconductor near the Berezinskii-Kosterlitz-Thouless transition
We analyze numerically how the voltage-current (V-I) characteristics near the
so-called Berezinskii-Kosterlitz-Thouless (BKT) transition of 2D
superconductors are affected by a random spatial Gaussian distribution of
critical temperature inhomogeneities with long characteristic lengths (much
larger than the in-plane superconducting coherence length amplitude). Our
simulations allow to quantify the broadening around the average BKT transition
temperature of both the exponent alpha in V I^alpha and of the resistance V/I.
These calculations reveal that strong spatial redistributions of the local
current will occur around the transition as either I or the temperature T are
varied. Our results also support that the condition alpha=3 provides a good
estimate for the location of the average BKT transition temperature, and that
extrapolating to alpha->1 the alpha(T) behaviour well below the transition
provides a good estimate for the average mean-field critical temperature.Comment: 18 pages; pdfLaTeX; 1 TeX file + 8 PDF files for figures
(figs.1,2,3a,3b,4,5a,5b,6
Resonant peak splitting for ballistic conductance in magnetic superlattices
We investigate theoretically the resonant splitting of ballistic conductance
peaks in magnetic superlattices. It is found that, for magnetic superlattices
with periodically arranged identical magnetic-barriers, there exists a
general -fold resonant peak splitting rule for ballistic conductance,
which is the analogy of the -fold resonant splitting for transmission in
-barrier electric superlattices (R. Tsu and L. Esaki, Appl. Phys. Lett. {\bf
22}, 562 (1973)).Comment: 9 pages, 3 figures, latex forma
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